The present invention relates to offshore stations, and more particularly to offshore stations moored at sea which are supported by floats.
In the prior art, it is known to have fixed or mobile stations, such as oil drilling rigs or scientific research stations located offshore because the item to be mined or studied is located offshore. Additionally, under present discussion, it is desired to locate power plants, and especially nuclear power plants, remote from shore, because of environmental and safety reasons.
In the case of nuclear power plants for the generation of electricity, an offshore station would have the capability of dumping the nuclear reactor's radioactive waste in the sea at various locations, thereby minimizing the buildup of radioactivity in one particular location.
All of the aforementioned offshore stations share the common problem that they have a submerged support structure which requires periodic maintenance. The sea environment attacks the support structure by mechanical erosion due to wave motion, chemical corrosion due to the presence of salt and other minerals found in sea water, and marine fouling due to the ever present growth of sea life, such as algae and seaweeds.
The prior art has attempted to deal with the maintenance problem by the technique of periodically ferrying the entire station to a home base on land for a complete overhaul. This approach has the obvious disadvantage of disturbing the work being performed by the station, as well as the further engineering problem of being very difficult to tow offshore stations of great physical size. It will be appreciated that in the case of a nuclear power plant which supplies electricity to a city, that it would be intolerable to stop the work of the station, as well as being virtually impossible to tow a station of such a great size.
The prior art has further dealt with the maintenance problem by periodically applying a layer comprised of chemical substances which are resistant to the corrosive effects of sea water. However, this approach suffers from the disadvantage that the chemical coats are only of limited stability; consequently, this approach results in relatively short time intervals between maintenance periods. Furthermore this approach does not deal at all with the marine fouling problem which is caused by the growth of sea life and which must be periodically scraped off.
The prior art also has utilized "sacrificial cathode" techniques. Different metals on the support structure having differing electrochemical conductive potentials will conduct an electrical current through the sea water due to the presence of salt and other minerals commonly found in the sea. In other words, an electrolysis reaction will take place with the different metals serving as the cathode and anode respectively, and the sea water acting as the electrolytic solution. A sacrifical cathode of higher electrical conductivity than one of the metals on the support structure is placed in closer proximity to the other metal, so that the electrolytic reaction will occur not between the metals of the support structure, but between the sacrificial cathode metal and only one metal of the support structure.
This approach suffers from the disadvantage that the sacrificial cathode eventually wastes away and must be replaced at very frequent intervals. Moreover, divers are needed to constantly replace the costly sacrificial cathode. In the case of power plants which create force fields and thermal gradients and other electrical effects, a practical and efficient application of sacrificial cathodes is very difficult, and indeed not even possible.
Another problem in the prior art is the technique to be utilized in supplying additional personnel, food supplies and equipment to the offshore station. Helicopters which are generally utilized for this function are extremely costly to operate, as well as having a limited cargo capacity.